The invention concerns a control device for adjusting a relative angular position of a driven shaft, particularly a camshaft of an internal combustion engine, according to the preamble of claim 1.
A control device of the pre-cited type is known from U.S. Pat. No. 5,483,930. Through an adequate positioning of the valve control piston of the control valve in a hold position by a control circuit it is assured that one of the chambers of the adjusting element of the control device is supplied with an additional quantity of hydraulic fluid for compensating fluid leakage and stabilizing the position of the adjusting piston of the adjusting element.
The object of the invention is to provide a control device for adjusting a relative angular position of a driven shaft, particularly a camshaft of an internal combustion engine, which device enables a compensation of fluid leakage in a hold position of the valve control piston without a controlled positioning of the valve control piston.
This and other objects of the invention, which will also become obvious from the following description of the invention, are achieved by the fact that, in a third adjusted position (hold position) of the valve control piston of the control valve of the control device of the invention, to compensate for fluid leakage from the pressure medium channel of the connection A, the resistance in the connection between the connections P and A is lower than the resistance in the connection between the connections P and B, whereas to compensate for fluid leakage from the pressure medium channel of the connection B, the resistance in the connection between the connections P and B is lower than the resistance in the connection between the connections P and A.
With a control device of this type, the phase angle of the camshaft of an internal combustion engine can be set by an angular displacement between the camshaft and the belt- or chain-driven drive pinion not only for two end positions, namely, a first adjusted position with the phase angle xe2x80x9cadvancexe2x80x9d and a second adjusted position with the phase angle xe2x80x9cdelayxe2x80x9d, but also for an intermediate, third adjusted position (hold position) in which the value of the phase angle lies between the two extremes.
When an intermediate phase angle corresponding to a third adjusted position of the valve control piston of the control valve of the control device is set, a medium drive torque of the internal combustion engine having a dynamic and a static component is applied to the camshaft and, thus, to the chambers of the adjusting element of the control device. The dynamic torque component is applied substantially uniformly to the two chambers thus assuring an alternating supply of hydraulic fluid thereto, while the static torque component loads only one of the two chambers and thus the pressure medium channel connected to this chamber and the associated working connection of the valve body of the control valve.
A force and torque analysis taking into consideration the structure of the control device and the internal combustion engine makes it possible to predict which of the chambers and, thus also, which of the pressure medium channels and working connections of the valve body will be loaded by the static component of the torque of the internal combustion engine. During operation of the control device, increased leakage of fluid is to be expected at the loaded pressure medium channel and the associated working connection.
By the inventive structural measures implemented in the control valve, it is achieved that, in an intermediate adjusted position (hold position), for stabilizing the valve control piston for setting an intermediate phase angle, the pressure medium channel and the associated working connection of the control valve which will predictably be loaded by the static torque component have a lower hydraulic resistance to the delivery connection P than the pressure medium channel and the associated working connection that are not loaded by the static torque component.
Due to the lower hydraulic resistance set at the loaded connection, a larger volume of hydraulic fluid is supplied to the loaded pressure medium channel for compensating leakage of hydraulic fluid. This, at the same time, also stabilizes the position of the piston of the adjusting element.
By the inventive structural measures implemented in the valve control piston and/or in the valve body of the control valve, it is achieved that a larger volume of hydraulic fluid is supplied to the pressure medium channel and the associated working connection of the control valve loaded by the static torque component for compensating for the fluid leakage that has occurred there. In contrast to the prior art, there is no need for an expensive and interference-prone positioning of the valve control piston by a control circuit. Rather, it is possible in the control device of the invention, to use a 4/3 proportional valve, known per se, with a structurally modified valve control piston and/or valve body and defined adjusted positions (first position xe2x80x9cadvancexe2x80x9d, second position xe2x80x9cdelayxe2x80x9d and third position xe2x80x9choldxe2x80x9d). Compared to the prior art, in the control device of the invention, the pressure rigidity of the control valve and the torque rigidity of the entire hydraulic system of the control device are improved.
In an advantageous embodiment of the invention, for compensating for fluid leakage, the delivery connection P is connected through a connecting duct to the loaded pressure medium channel of the respective working connection of the control valve, so that more hydraulic fluid is supplied to this pressure medium channel than to the other channel. Such a connecting duct having a by-pass function can also be added subsequently to the control valve without structural modifications to the valve control piston and/or the valve body. The arrangement of a throttle in the connecting duct assures that a larger amount of hydraulic fluid is supplied to the loaded pressure medium channel as a compensation for leakage, above all when there is a higher working pressure at the delivery connection, and a back flow of hydraulic fluid from the pressure medium channel toward the delivery connection is also substantially prevented.
According to a further advantageous proposition of the invention, the connecting duct further comprises a one-way valve to reliably prevent a back flow of hydraulic fluid from the loaded pressure medium channel to the delivery connection. By a series connection of a throttle and a one-way valve in the connecting duct, the advantageous features of these can be jointly utilized. Alternatively, it is also possible to use a one-way valve having an adjustable biasing force. As an alternative or as a supplement to an external connecting duct between the delivery connection and the loaded pressure medium channel, a compensation for fluid leakage at this channel can also be effected with the control device of the invention by implementing suitable structural measures in the valve body and/or the valve control piston of the control valve.
In a further advantageous embodiment of the invention, the grooves and control regions of the valve control piston that is configured as a sliding piston can be arranged so that, in a third adjusted position (hold position), for realizing an intermediate phase angle of the camshaft, a lower hydraulic resistance prevails between the delivery connection of the control valve and the working connection of the loaded pressure medium channel, and, due to the resulting larger flow volume of hydraulic fluid compared to the connection between the delivery connection and the working connection of the non-loaded pressure medium channel, a compensation for fluid leakage at the loaded pressure medium channel takes place. In a control valve having a delivery connection arranged centrally between the two working connections, the grooves of the valve control piston can be arranged asymmetrically relative to a central axis of the delivery connection, so that in the hold position of the valve control piston, due to this groove arrangement, a lower hydraulic resistance prevails between the delivery connection and the loaded working connection than between the delivery connection and the non-loaded working connection. A compensation for fluid leakage at the loaded pressure medium channel and the associated working connection can also be effected by configuring the control edges of the valve body and/or the control regions of the valve control piston with different geometric shapes (e.g. chamfers, notches, curvatures etc.). The control edges of the valve body and/or the control regions of the valve control piston, for example, can have different radii of curvature.
The control valve of the invention serves particularly for the actuation of the adjusting element of a control device for the relative angular adjustment of a driven shaft, particularly a camshaft of an internal combustion engine. To effect a compensation for fluid leakage occurring at the loaded pressure medium channel of a working connection, the control valve can have the features described in connection with the control device of the invention. Neither the control device of the invention nor the control valve of the invention is restricted in use to adjusting elements functioning according to a particular principle of operation. The described control device and control valve can be used in camshaft adjusters both of an axial and a radial piston type.